That ongoing debate was thrown into a nightmarish spotlight this week. Police say Nasim Aghdam, a 39-year-old woman who posted clips about veganism and music video parodies, drove to YouTube's San Bruno, California, headquarters Tuesday, walked onto its sunny campus through a parking garage and shot three people before killing herself.

We don't know why Aghdam fired on people at YouTube. But law enforcement officials have established that her motive was anger at the company's policies and practices.

Influential YouTubers like Hank Green and Phil DeFranco, the latter of whom has been a vocal critic of some YouTube policies in the past, spoke out against conflating the shooter's motive with the idea that Google's site or its policies were at fault for the crime.

"This has nothing to do with YouTube policy. It's a sad and horrific story of a person who built anger and hate inside of herself until it seemed like a good idea to get a gun and use it," Green, one half of the Vlog Brothers, said on Twitter on Wednesday.

But Tuesday's tragedy and Aghdam's ire toward YouTube have made insider topics, like demonetization, something that everyday YouTube watchers are trying to understand.

The stakes are nothing less than YouTube's responsibility to check the spread of abusive content on its gigantic platform, where 400 hours of content are uploaded every minute, while preserving the free flow of creativity there, without which YouTube may never have grown into the biggest video site on the planet.

What is demonetization?

Creators and others who post video on YouTube, if they meet certain qualifications (more on that below), can opt to make money by allowing advertising to run with their clips. That's called monetization. But YouTube has policies about what's allowed to carry advertising, because marketers don't want their ads running against objectionable stuff, like pornography, profanity or videos that incite hatred. For the full details, here are YouTube's AdSense Program Policies.

YouTube CEO Susan Wojcicki has said that drawing a line about what's appropriate on YouTube is sensitive because "on one side is censorship and the other is too much freedom of speech."

Noam Galai/YouTube

If YouTube determines that a video violates these policies, it can strip the clip of its advertising and pull the plug on any more money flowing in. If a channel is a repeat offender, it can be kicked out of monetization altogether. But clips can be demonetized and still be OK to exist on YouTube. The company also has terms of service and community guidelines that outline what kinds of videos YouTube may take down completely.

In January, YouTube tightened its standards for channels to qualify for advertising. To join what is known as the YouTube Partner Program, channels must have 1,000 subscribers and have accumulated at least 4,000 hours of watch time in the past 12 months. The previous threshold required channels to acquire 10,000 total views to be eligible for the program.

Responding to a request for comment, YouTube didn't address the issue of demonetization. Instead, it pointed to its Wednesday statement.

That statement read, in part: "Yesterday's horrific act of violence was deeply shocking and disturbing to our YouTube Family. Still, we are uplifted by the heroic acts we witnessed both from employees and the San Bruno community, especially the first responders. ... We want to express our deepest gratitude to the first responders, including the police, fire department and medical response teams. And a huge thank you also to the wider global community for their outpouring of support, well wishes and words of togetherness."

What's 'adpocalypse'?

Last spring, after media reports exposed examples of YouTube's automated software sticking ads next to clips heavy on racism or other objectionable content, angry advertisers -- including giant brands like Pepsi, Walmart and AT&T -- pulled out of YouTube in a widespread boycott.

When YouTube responded by more aggressively demonetizing sensitive clips, it ended up outraging people who uploaded videos that seemed fine but still inexplicably lost their moneymaking power -- an event creators dubbed "adpocalypse."

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Since then, "adpocalypse" has been the term to describe what some creators say is an ongoing problem of YouTube improperly demonetizing harmless videos.

In some cases, this could be the annoying loss of extra cash. But in other instances, it could threaten creators' livelihoods.

Which YouTube policies motivated the shooter?

We don't know. We also don't know for certain whether her videos were demonetized.

But San Bruno police said Wednesday that Aghdam, who reportedly lived in San Diego, was upset about YouTube's policies and practices and that was the motive they identified for the shooting at its headquarters. Local law enforcement hasn't updated the public with further details about her motive since then.

Hank Green, right, and his brother John co-founded Vidcon, one of the biggest conventions of YouTube fans and creators. Hank Green has criticized conflating the shooter's motive with the idea YouTube policies were at fault for the crime.

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From Aghdam's website and social channels and from published interviews with her family, we know that she was angry at YouTube and Google for perceived suppression. Her English-language YouTube channel was even titled "Nasim Vegan Suppressed" as of 2016, the latest time her page was scraped by the Internet Archive.

(Aghdam's pages on YouTube and other social networks, as well as her personal website, have been taken down in the wake of the shooting.)

In an interview with the Mercury News, the shooter's father said she "hated" YouTube because she felt censored and wasn't able to earn money off advertising. Posts on her website claimed that YouTube placed age restrictions on her content -- this "age gating" means videos aren't visible to people who are logged out, are younger than 18 or have Restricted Mode enabled -- and that the service was "filtering" her clips to reduce views and discourage her from making more.

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